Resistance-unit.



PATENTED MAR. 24, 1908.

L. E. BARRINGBR.

RESISTANCE UNIT.

APPFIOATION FILED 8EPT. 30. 1907.

4mm Om 9n. M m \E. mm H e r W nu L VJ \D tion of material UNITED STATES PATENT OFFICE.

4 LAWRENCE E. BARRINGER, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

RESISTANCE-UNIT.

Specification of Letters Patent.

Patented March 24, 1908.

Application filed September 30, 1907. Serial No. 395,130.

To all whom it my concern.-

Be it known that I, LAWRENCE E. BAR- RINGER, a citizen of the United States, residing at Schenectady, county of Schenectady, State of New York, have invented certain new and useful Improvements in Resistance- Units, of which the following is a specification.

My invention relates to a new combination of material for use in the production of a resistance stick or unit. This new combinaroduces results not heretofore attainedwit i resistance sticks, and renders possible a wider a plication of said sticks, as will be further Fescribed.

The accompanying sketch shows an application of these resistance units or members in lightning arresters, but their use may be extended to rheostats, car heaters, fan motors resistances, and so forth, and in fact, to any electrical use where a uniform resistance is required.

Figure 1 is a front view of a wellknown form of lightning arrester, and 2 is a side view of the same.

'The non-inductive resistance 1 and the metal cylinders 2, 3 of this arrester form part of a grounded circuit. A current of very high potential such as a lightning discharge, wil jum the gap between 2 and 3 and e rounde TlllS form of li htning arrester 1s well-known and hence wilI require no further description here. For the non-inductive resistance 1, I propose to use the resistance member or unit hereinafter described.

As a novel in edient of my resistance unit I use a materia well known to the trade as alundum. Alundum is a very hard, crystalline material made from bauxite, an amorphous hydrate of aluminium, by a process of urification and electric furnace treatment.

he material resulting from this treatment is essentially a'fused alumina, of a high degree of purity and uniformity. It is a sort of artificial corundum composition, as it corresponds in general to the chemical formula A1 0 The alundum is mixed in various proportions with clay and graphite according to the roperties desirer in the finished product. Phave used the following proportions in preparing my resistance unit. 20 parts alundum, 20 )arts fire clay (with which may be mixed, if desired, suitable amountsof feldspar and flint); 1% to 2% parts of graphite. As the graphite is added to give the stick conductivity, its roportion is variable. These materials are oroughly mixed, preferably wet, squirted into shape,

dried and baked at a temperature of 1100 degrees to 1300 degrees. The sticks may be enameled with any known enamel to keep out moisture. Contact surfaces may be made at each end in any known way, such as carbonizing the ends, co per-plating them, shrinking on them meta ca 8, or the like. Each ingredient mentioned a ove has a positive and regular effect on the ultimate product. The alundum gives the unex ectedly beneficial results hereinafter set fort fi graphite serves to give the requisite conductivity, and the clay base serves as a binding material to form a strong, compact rod or stick. As a clay hinder or base, I prefer to employ a high grade fire clay. If a more vitreous mass should be desired, an admixture of feldspar and flint may be made, as above mentioned.

I am aware thata combination of carborundum, clay base and graphite has been used in the production of a resistance stick but the use of this material was accompanied with certain disadvantages. The reslstance of a rod containing this material changes in an irregular manner during heating. The resistance is generally higher on cooling. than originally, sometimes lower, and only rarely does it approximate the original resistance' This fact alone barred out the use of these resistances in rheostats and other applications.

When alundum is employed instead of car borundum, I find that the resistance of the rods remains constant after heating. I con- .sider this difference of behavior a most important one. While I do not wish to belimited by any particular theory I believe the behavior of carborundum rods may beattributed to the fact that the expansion and contraction of these rods in heating and cooling brings about a readjustment of the partic es and a change in the contact of the con- The.

ducting articles throughout the mass. .As

the coe cient of expansion of alundum is almost zero, these readjustments may not oc cur when this material is'heated and cooled. Furthermore, it was found that the conductivity of the raw carborundum varied greatly. Hence, in order to make a rod of a given resistance, it was first necessary to determine the conductivity of the carborundum by preliminary experiments. This being determined, more or less graphite was added in the manufacture of the rod, according to the determined conductivity of the carborundum. This consumed time and involved expense.

With alundum we have a material whose conductivity is constant, that is, it is practically zero. Therefore in order to roduce a given conductivity in the finishe rod, a certain definite amount of graphite as an ingredient is added Without the necessity for previous analysis.

A further advantage in the use of alundum instead of carborundum as an ingredient lies in the fact that the finished alundum sticks are less liable to crack and burst when heated to a hi h temperature. As is well known, the carborundum sticks crack and burst on heating to a high temperature.

In addition to the desirable qualities set forth, I find the alundum resistance sticks are tou her and stronger than the sticks made with carborundum. In the carborundum stick the clay base was ractically the only source of strength, there ore, the prop- Vl dum, graphite and fire clay.

2. A resistance member consisting of fused alumina, refractory conducting material, and a suitable binder. I

3. A resistance member consisting of a .mixture of alundum, graphite and clay.

4. A resistance member consisting of parts of alundum, 20 arts of clay base, and 1 to 2% parts of grap 'te.

5. The combination of a resistance member consisting of alundum, graphite, and clay, an enamel upon the surface of said member, and means for makin' electrical contacts with the ends of said ro s.

In witness whereof I have hereunto set my hand this 28th day of September, 1907 LAWRENCE E. BARRINGER.

Witnesses: BENJAMIN B. HULL, HELEN ORFORD. 

